This invention relates to optical apparatus for carrying information and, more particularly, to apparatus for controlling the wavelength of an optical source for encoding such information.
As fiber optics techniques have matured, a great deal of attention is now being paid to the wavelength division multiplexing (WDM) technique for encoding and sending information. In wavelength division multiplexing, several different optical wavelengths are multiplexed to create a single composite signal for transmission down a single optical fiber. For example, information may be impressed upon three separate wavelengths .lambda..sub.1, .lambda..sub.2 and .lambda..sub.3. These three signals are then multiplexed to create a composite signal which can travel down a single optical fiber. At the receiving end, the composite signal is demultiplexed into the individual signals .lambda..sub.1, .lambda..sub.2 and .lambda..sub.3 and each of these signals is demodulated to extract the impressed information. Wavelength division multiplexing offers many advantages including increased bandwidth and reliability as well as reduced size and cost. It is known that source wavelength stability is crucial in order to maintain nominal operation of such systems. In the above example, it is thus important that the source wavelengths .lambda..sub.1, .lambda..sub.2 and .lambda..sub.3 remain stable over time. Drift of the center peak wavelengths of the input sources can cause unacceptable increases in cross-talk among the signals as well as high signal insertion losses.
It is therefore an object of this invention to provide apparatus for controlling the wavelength of optical sources used, for example, in wavelength division multiplexing.
It is a further object of this invention to provide such apparatus which employs a feedback loop to control the optical source peak wavelenth.
Yet another object of this invention is control apparatus which is highly accurate, simple and reliable in operation.